In a conventional light emitting device, a buffer layer, an N-type semiconductor layer, an active layer and a P-type semiconductor layer are sequentially formed on a substrate. The P-type semiconductor layer and the active layer are dry-etched through a photolithographic process to expose the substrate such that a plurality of light emitting cells with a certain size are isolated from one another on the substrate. A metal layer for ohmic contact is formed on the N-type and P-type semiconductor layers. A metal film is deposited through a photo process so as to electrically connect the exposed N-type metal layer and a region exposed on the P-type metal layer of adjacent light emitting cells, and a conductive material such as gold (Au) connects the adjacent light emitting cells in the air through an air bridge process.
Thereafter, a metal bump is formed to have a thickness of about 5 to 30 μm in a region on the P-type metal layer by means of a method such as plating, thereby completing fabrication of a substrate. The device substrate fabricated as above is divided on an isolated light emitting cell basis, and flip bonding is performed such that the top of the light emitting cell is bonded to the surface of a patterned submount substrate. Thereafter, the submount substrate is cut into a certain size to be in the form of a flip chip. Each submount substrate is die-bonded on a package substrate for assembling, and an electrode of the package substrate is connected to a bonding pad on the submount substrate through a metal wire, thereby completing an alternating current (AC) flip chip.
Such an AC light emitting device has electrodes respectively connected in parallel in two different directions, and is operated in such a manner that a light emitting device array connected in a forward direction is lighted in a forward bias and a light emitting device array connected in a reverse direction is lighted in a reverse bias when the AC light emitting device is connected to an AC power source.
However, since such integrated AC light emitting cell arrays are connected in two different directions, a leakage current may flow through some of the light emitting cells of one of the light emitting cell arrays when a current flows in a forward direction and thus the light emitting cell array is lighted. At this time, the flow of an excessive current due to excessive voltage drop in the subsequent light emitting cells causes ununiform light emission of the light emitting cells, damage to the light emitting cells and shortened life span thereof.
The present invention is conceived to solve the aforementioned problems. Accordingly, an object of the present invention is to provide a light emitting device, wherein even though an excessive current occurs in some of light emitting cells, the current is allowed to cross light emitting cells connected in another direction.
Another object of the present invention is to provide a light emitting device capable of ensuring uniform light emission and prolonged life span in an AC light emitting device.
To achieve the objects, a light emitting device of the present invention comprises a substrate; and first and second light emitting cell blocks formed on the substrate and having a plurality of light emitting cells electrically connected in series to one another, respectively. Each of the light emitting cells has an N-electrode and a P-electrode. A P-electrode at one end of the first light emitting cell block is connected to an N-electrode at one end of the second light emitting cell block, and an N-electrode at the other end of the first light emitting cell block is connected to a P-electrode at the other end of the second light emitting cell block. The P-electrode of each of the light emitting cells of the first light emitting cell block and the P-electrode of each of the light emitting cells of the second light emitting cell block corresponding thereto, or the N-electrode of each of the light emitting cells of the first light emitting cell block and the N-electrode of each of the light emitting cells of the second light emitting cell block corresponding thereto are electrically connected to each other. The light emitting device may further comprise a submount substrate flip-bonded to the first and second light emitting cell blocks. Metal pads may be formed between the submount substrate and the respective light emitting cells.
Moreover, metal wires may be formed on the submount substrate, and the P-electrode of each of the light emitting cells of the first light emitting cell block and the P-electrode of each of the light emitting cells of the second light emitting cell block corresponding thereto, or the N-electrode of each of the light emitting cells of the first light emitting cell block and the N-electrode of each of the light emitting cells of the second light emitting cell block corresponding thereto may be electrically connected to each other through the metal wires.
The light emitting cell may comprise an N-type semiconductor layer formed on the substrate; a P-type semiconductor layer formed in a region on the N-type semiconductor layer; and an N-electrode and a P-electrode formed on the N-type and P-type semiconductor layers, respectively.